Armed officers have arrested a man in connection with preparing a terror attack just yards from Downing Street.

Police say the 27-year-old was carrying a rucksack containing several knives, which are being examined by forensic officers.

The suspect was known to police prior to his arrest, according to Sky sources.

Image:A man is led away by police in Westminster after an arrest was made on Whitehall

Roads were locked down as officers carried out the arrest – pushing the man to the ground before holding him at the scene. No one was injured in the incident, and Whitehall has since reopened northbound.

The Metropolitan Police said the man was stopped at 2.22pm as part of an ongoing operation. He has been taken to a south London police station where he is being held under the Terrorism Act.

He was arrested on the Parliament Street junction with Parliament Square, close to the scene of last month’s terror attack which killed five people including PC Keith Palmer on 22 March.

Image:The Prime Minister campaigning outside of London at the time of the incident

Theresa May was not at Number 10 at the time of the incident.

Speaking from a General Election campaign event in Derbyshire, the Prime Minister said: “I’m aware that a man has been arrested in Whitehall today and that individual has been arrested on the basis of a terrorism charge.

“I think it shows that our police and intelligence and security services are on alert as they always are – looking to keep us safe and secure. I would say we owe a huge debt of gratitude to these people.”

Image:A forensic investigator recovers a knife after man was arrested on Whitehall in Westminster, central London

London Mayor Sadiq Khan tweeted: “Thanks to all officers who dealt swiftly & professionally with the incident in Whitehall. The Met Commissioner has briefed me on the arrest.”

A Metropolitan Police statement said: “The man, aged in his late twenties, was arrested on suspicion of possession of an offensive weapon and on suspicion of the commission, preparation and instigation of acts of terrorism.

“Knives have been recovered from him.

“Detectives from the Counter Terrorism Command are continuing their investigation, and as a result of this arrest there is no immediate known threat.”

Sky News Political Correspondent Lewis Goodall said: “A witness said at one point he was taken to the ground – he was wearing a black tracksuit. Police surrounded him.

“There are various police officers here, both armed guards and forensic officers who are examining the scene. Earlier, we managed to get in the thick of it and we could see a bag clearly with a selection of knives which are being examined.

Image:The moment the suspect was arrested

“This is one of the busiest thoroughfares in London, you’ve got thousands and thousands of people working in government departments among other things and the area has come to something of a standstill.”

A builder working on the road nearby said: “I saw the police officers catch him. They caught him and got him on the ground.”

Asked if the suspect was waving knives, acting aggressively or shouting, the witness said: “No.”